1. Field of the Invention
The present invention relates to a method of designing a semiconductor integrated circuit such as a standard cell.
2. Description of Related Art
Automated design techniques for semiconductor integrated circuits have recently improved so much, this automatic design is widely used in the semi-customization of components such as standard cells. In the automatic design, automated routing is used for the power wires. This makes it possible to reduce the manual labor required by the routing of power wires.
However, it is necessary for the designers to do some manual labor, even with automated routing. In other words, if a VDD power wire and a VSS power wire should overlap after the automated routing, by way of example, the designers much adjust that portion manually. This causes an increase in the time required for routing the power wire.
An objective of the present invention is to provide a method of designing a semiconductor integrated circuit that makes it possible to reduce, or even eliminate, the manual work that must be done by the designers during the automated routing of a power wire.
The present invention relates to a method of designing a semiconductor integrated circuit including a circuit block, the method comprising:
a step of placing the circuit block;
a step of routing a power wire for a circuit block that supplies power to the circuit block, the power wire including a first edge extending in a first direction and a second edge extending in a second direction; and
a step of selecting a first-direction power wire to be routed in a first direction by automated routing, after the step of routing the power wire for a circuit block, taking into consideration a position of the power wire for a circuit block.
Since this aspect of the invention ensures that the position of a power wire for a circuit block is determined first, the first-direction power wire can be selected from consideration of the position of the power wire for a circuit block. For that reason, it is possible to reduce or even eliminate the manual work of correcting the first-direction power wire, after the first-direction power wire has been routed automatically. Note that the step of placing circuit block and the step of routing the power wire for a circuit block can be done in either order or could be done simultaneously.
The present invention further relates to a method of designing a semiconductor integrated circuit including a circuit block, the method comprising:
a step of placing an I/O port;
a step of placing the circuit block;
a step of routing a power wire for a circuit block that includes a first edge extending in a first direction and a second edge extending in a second direction and supplies power to the circuit block; and
a step of selecting a first-direction power wire that is routed by automated routing and is connected to the I/O port, after the step of routing the power wire for a circuit block, from consideration of a position of the power wire for a circuit block.
Since the position of the power wire for a circuit block is determined first in accordance with this aspect of the invention, the first-direction power wire to be connected to the I/O port can be selected from consideration of the position of that power wire for a circuit block. For that reason, it is possible to reduce or even eliminate the manual work of the designers during the automated routing of the first-direction power wires. Note that the step of placing the I/O port, the step of placing circuit block, and the step of routing the power wire for the circuit block can be done in any order or could be done simultaneously.
The present invention still further relates to a method of designing a semiconductor integrated circuit including a circuit block, the method comprising:
a step of placing the circuit block; and
a step of selecting a power wire to be routed by automated routing, after the step of placing the circuit block, from consideration of a position of the circuit block.
Since the position of the circuit block is determined first in accordance with this aspect of the invention, the power wire can be selected from consideration of the position of the circuit block. For that reason, it is possible to reduce or even eliminate the manual work of the designers during the automated routing of power wires. This aspect of the present invention may comprise: a step of routing a power wire for a circuit block that supplies power to the circuit block, before the step of selecting a power wire. In this aspect of the present invention, the power wire for a circuit block may comprise a first edge extending in a first direction and a second edge extending in a second direction. In this aspect of the present invention, the power wire that is routed by automated routing may be a first-direction power wire extending in a first direction.
In the present invention, the step of selecting the first-direction power wire may select a power wire at a position that enables connection to the second edge. Here, the power wire for a circuit block and the first-direction power wire may be VDD power wires or VSS power wires. Note that the first-direction power wire and the second edge of the power wire for a circuit block are positioned in separate upper and lower layers, so that connection therebetween is done by a conductive layer formed in a through hole.
In the present invention, the step of selecting the first-direction power wire may perform the selection in a manner to avoid a wire at a position that overlays the first edge. The meaning thereof is discussed below. Assume that the first direction is the y-axis direction, by way of example. When the x-coordinate of a first-direction power wire is the same as that of the first edge of the power wire for a circuit block, these two wires are in the same layer so the first-direction power wire overlays the first edge of the power wire for a circuit block. For that reason, when the power wire for a circuit block is a VDD power wire and the first-direction power wire is a VSS power wire, by way of example, it is not possible to route the first-direction power wire. In such a case, it is determined to not-select this first-direction power wire. In the present invention, the power wire for a circuit block may be a VDD power wire and the first-direction power wire may be a VSS power wire, or the power wire for a circuit block may be a VSS power wire and the first-direction power wire may be a VDD power wire.
The present invention may further comprise a step of automatically routing the first-direction power wire, after the step of selecting the first-direction power wire.
In the present invention, the power wire for a circuit block may comprise an encircling power wire. An encircling power wire is a power wire such that one end portion is connected to the other end portion thereof. The shape of the encircling power wire could have a circular frame or a quadrilateral frame, by way of example.
In the present invention, the circuit block may comprise at least one of ROM, RAM, an analog circuit, a control circuit, and an interface circuit.
In the present invention, the semiconductor integrated circuit may comprise at least one of a standard cell, a gate array, and an embedded array.